The present invention relates to image processing and, in particular, to adaptive sharpening of an image.
Applications that use and display compressed video often must prepare video for transmission over a communications pipeline such as ordinary phone lines (i.e., Plain Old Telephone Service) (POTS)) or Integrated Services Digital Network (ISDN), which provide a limited bandwidth through which the video must be transmitted. This limitation on the bandwidth imposes a qualitative upper bound on the video compressed with state of the art algorithms. Additionally, when the communication is over POTS, the size of the frames are typically limited. In general, the compressing of data is a lossy process and a consequence thereof is the manifestation of compression artifacts which are products introduced into the image as a result of compression that do not exist otherwise. Moreover, data compression subjects the image to a general loss of detail. Despite these limitations, application users, typically, want bigger video images (i.e., images occupying a significantly greater percentage of the display screen area).
When images are small, the eye is forgiving. However when scaling images to larger sizes, the small defects (e.g., the artifacts or loss of detail and texture) due to the compression become extremely visible causing the image to frequently appear xe2x80x9cwashed outxe2x80x9d as the same information is spread over a larger area. To avoid this xe2x80x9cwashed outxe2x80x9d effect, sharpening post filters are applied to help bring some more definition and crispness to images. However, compression artifacts, such as ringing, must be taken into account during the sharpening process. Otherwise, these defects are magnified along with the image causing the image to look even worse than if no sharpening was performed. Therefore, for these and other reasons there is a need to identify the undesirable compression artifacts within an image and obviate their amplification during the sharpening process through adaptive sharpening of an image which sharpens all of the image excluding the identified undesirable compression artifacts.
In one embodiment, a method includes decoding a video image such that the decoding generates a number of transform coefficients. Additionally, the number of transform coefficients are processed to determine whether to sharpen the video image.